This invention relates to variable capacity vane compressors which are adapted for use as refrigerant compressors of air conditioners for automotive vehicles.
A variable capacity vane compressor is known e.g. by Japanese Provisional Utility Model Publication (Kokai) No. 55-2000 filed by the same assignee of the present application, which is capable of controlling the capacity of the compressor by varying the suction quantity of a gas to be compressed. According to this known vane compressor, arcuate slots are formed in a peripheral wall of the cylinder and each extend from a lateral side of a refrigerant inlet port formed through the same peripheral wall of the cylinder and also through an end plate of the cylinder, and in which is slidably fitted a throttle plate, wherein the effective circumferential length of the opening of the refrigerant inlet port is varied by displacing the throttle plate relative to the slot so that the compression commencing position in a compression chamber defined in the cylinder varies and accordingly the compression stroke period varies to thereby vary the capacity or delivery quantity of the compressor. A link member is coupled at one end to the throttle plate via a support shaft secured to the end plate, and at the other end to an actuator so that the link member is pivotally displaced by the actuator to displace the throttle plate.
However, according to the conventional vane compressor, because of the intervention of the link member between driving means or the actuator and a control member or the throttle plate for causing displacement of the throttle plate, the throttle plate undergoes a large hysteresis, leading to low reliability in controlling the compressor capacity, and also the capacity control mechanism using the link member, etc. requires complicated machining and assemblage.
Further, a variable capacity vane compressor which has a reduced hysteresis of the control member has been proposed by Japanese Provisional Patent Publication (Kokai) No. 61-232397 filed by the same assignee of the present application, which provides an improvement in a vane compressor comprising a cylinder formed of a cam ring and a pair of side blocks closing opposite ends of the cam ring, a rotor rotatably received within the cylinder, a plurality of vanes radially slidably fitted in respective slits formed in the rotor, a control member disposed for displacement in a refrigerant inlet port formed in one of the side blocks, and driving means for causing the control member to be displaced relative to the refrigerant inlet port, whereby the capacity or delivery quantity of the compressor can be varied by displacement of the control member. The improvement comprises driven teeth provided on the control member, and driving teeth provided on an output shaft of the driving means in mating engagement with the driven teeth, whereby the control member is driven directly by the driving means through the mating driving and driven teeth.
However, according to this conventional vane compressor, a stepping motor as the driving means is mounted within the compressor housing, requiring a large space for accommodation of the stepping motor, and the capacity control mechanism has an overall complicated construction and accordingly is high in manufacturing cost.
A variable capacity vane compressor attempting to improve the above-discussed problems has been proposed by Japanese Utility Model Application No. 60-183319 filed by the same assignee of the present application, which provides an improvement in a vane compressor comprising a cam ring having opposite axial ends closed by respective side blocks, a rotor rotatably received in the cam ring, and vanes slidably fitted in respective vane slits formed in the rotor, wherein fluid is compressed by change in volume of compression chambers respectively difined by the rotor and the adjacent vanes. The improvement comprises a pair of second inlet ports provided in one of the side blocks which has the inlet port, a pair of spaces provided in the one side block and communicating with a low pressure zone and a high pressure zone, a control element having a pair of pressure-receiving protuberances axially projecting from axial one end face of the control element, each of the pressure-receiving protuberances being slidably fitted in a corresponding one of the spaces to divide the space into a first pressure chamber communicating with the low pressure zone and a second pressure chamber communicating with the high pressure zone, the control element being fitted in an annular recess provided in the one side block for angular movement in opposite circumferential directions, for controlling opening angles of the respective second inlet ports, an integrally molded sealing member formed of an elastic rubber and mounted to the control element for sealing between the respective first pressure chambers and the respective second pressure chambers and between the low pressure zone and a zone of a back pressure acting upon the vanes, a communication passageway communicating the respective second pressure chambers with the low pressure zone, and a control valve device provided in the communication passageway and operable to close same when the pressure in the low pressure zone is above a predetermined value and to open the communication passageway when the pressure in the low pressure zone is below the predetermined value, wherein the control element angularly moves in response to the differential pressure between the first and second pressure chambers to control the opening degrees of the respective second inlet ports, to thereby control the compression commencing timing to vary the capacity or delivery quantity of the compressor.
However, the above-described conventional variable capacity vane compressor has such a problem that a hysteresis is large between the rotative shift of the control element toward the full capacity operation side (the side of increase in delivery quantity) and the rotative shift of the control element toward the partial capacity operation side (the side of decrease in delivery quantity). The reason for this is that torque due to the resistance of the sealing member, i.e., seal resistance acts as a reaction force against torque acting upon the control element when shifting toward the full capacity operation side (torque due to the pressure within the second pressure chambers of the respective spaces, hereinafter referred to as "pressure torque"), and against torque acting upon the control element when shifting toward the partial capacity operation side (torque due to a spring urging the control element toward the partial capacity operation side, hereinafter referred to as "spring torque"). The torque due to the seal resistance causes the hysteresis.
In order to reduce the hysteresis, the "pressure torque" and "spring torque" against the seal resistance torque should respectively be increased.
In order to increase the former "pressure torque", it is required to increase control pressure acting upon the control element, i.e., the pressure within the second pressure chambers of the respective spaces, or to increase the pressure-receiving areas of the respective pressure-receiving protuberances. In this connection, the pressure within the second pressure chambers of the respective spaces, which is the aforesaid control pressure, is determined dependent upon the cooling cycle, and the force of the spring is set to a value corresponding to the control pressure. Therefore, it becomes necessary to increase the pressure-receiving areas of the respective pressure-receiving protuberances.
The sealing member in the variable capacity vane compressor according to the aforementioned Japanese Utility Model Application No. 60-183319 comprises, as shown in FIG. 1 of the accompanying drawings, a first annular sealing portion 80a fitted in a groove 83 formed in the axial one end face of the control element 81 and extending along a peripheral edge of a central bore 82 formed in the control element 81, for sealing between a central portion of the axial one end face of the control element 81 and a bottom wall surface of an annular recess formed in the side block, not shown, a pair of second sealing portions 80b in the form of an arc concentric with the first sealing portion 80a and fitted respectively in a pair of grooves 84 provided along an outer peripheral edge of the axial one end face of the control element 81 for sealing between the outer peripheral portion of the axial one end face of the control element 81 and the bottom wall surface of the annular recess in the side block, a pair of third sealing portions 80c in the form of a flat plate and provided in a manner integral with respective ends of the respective second sealing portions 80b and the first sealing portion 80a to connect them with other, the third sealing portions 80c being fitted respectively in grooves 86 formed in the respective pressure-receiving protuberances 85 on the control element 81 for sealing between the outer peripheral side surfaces of the respective pressure-receiving protuberances 85, and the annular recess and the spaces in the side block, and a pair of fourth sealing portions 80d provided in a manner integral with the respective other ends of the respective second sealing portions 80b and the first sealing portion 80a to connect them with each other, the fourth sealing portions 80d being fitted respectively in a pair of generally radially extending prooves 87 formed in the axial one end face of the control element 81 to seal between the axial one end face of the control element 81 and the bottom wall surface of the annular recess in the side block. That is, since the sealing structure for the control element 81 is of a plane seal at only the axial one end face thereof, the pressure-receiving protuberances 85 must be disposed between the first sealing portion 80a and the respective second sealing portions 80b. In order to increase the pressure-receiving areas of the respective pressure-receiving protuberances 85, it is required to increase the axially protruding length L.sub.1 of each protuberance 85, or to increase the lateral width L.sub.2 thereof. However, if the protruding length L.sub.1 is increased, the compressor is increased in axial length correspondingly. On the other hand, the increase in the lateral width L.sub.2 results in increase in the length of the longitudinal side of each third sealing portion 80c of the sealing member 80, the length of each fourth sealing portion 80d, and the length of each second sealing portion 80b. This increases the sealing line length along these portions, causing increase in the seal resistance. Accordingly, it is not possible to increase the pressure-receiving areas of the respective pressure-receiving protuberances 85 without increase in the axial length of the compressor and without increase in the sealing line length. Further, the sizes or dimensions La, Lb and Lc of various portions of the sealing member 80 must be controlled, so that high precision is required for the manufacture of the sealing member 80.
Moreover, all of the sealing surfaces of the respective portions of the sealing member 80 are located at the axial one end face or front face of the control element 81. Therefore, if the control element 81 is subjected to an axial force due to the pressure acting thereupon and is displaced axially, the urging force acting upon the sealing member 80 varies, causing change in the air-tightness due to the sealing member 80 and the slidability of the control element 81.